ASTM D792-98

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: D 792 – 98
Standard Test Methods for
Density and Specific Gravity (Relative Density) of Plastics
by Displacement
This standard is issued under the fixed designation D 792; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope * E 380 Practice for Use of the International System of Units
(SI) (the Modernized Metric System)
1.1 These test methods describe the determination of the
E 691 Practice for Conducting an Interlaboratory Study to
specific gravity (relative density) and density of solid plastics
Determine the Precision of a Test Method
in forms such as sheets, rods, tubes, or molded items.
1.2 Two test methods are described:
3. Terminology
1.2.1 Test Method A—For testing solid plastics in water, and
3.1 General—The units, symbols, and abbreviations used in
1.2.2 Test Method B—For testing solid plastics in liquids
these test methods are in accordance with Practice E 380.
other than water.
3.2 Definitions:
NOTE 1—Alternatively, Test Method D 1505 may be applied to many
3.2.1 specific gravity (relative density)—the ratio of the
such forms, as well as to films and sheeting.
mass in air of a unit volume of the impermeable portion of the
1.3 The values stated in SI units are to be regarded as the
material at 23°C to the mass in air of equal density of an equal
standard.
volume of gas-free distilled water at the same temperature. The
1.4 This standard does not purport to address all of the
form of expression shall be:
safety concerns, if any, associated with its use. It is the
Specific gravity ~relative density! 23/23°C
responsibility of the user of this standard to establish appro-
~or sp gr 23/23°C!
priate safety and health practices and determine the applica-
NOTE 3—This definition is essentially equivalent to the definition for
bility of regulatory limitations prior to use.
apparent specific gravity and apparent density in Terminology E 12,
because the small percentage difference introduced by not correcting for
NOTE 2—There is no similar or equivalent ISO standard.
the buoyancy of air is insignificant for most purposes.
2. Referenced Documents
3.2.2 density—the mass in air in kilograms per cubic metre
2.1 ASTM Standards:
of impermeable portion of the material at 23°C. The form of
D 618 Practice for Conditioning Plastics and Electrical
expression shall be:
Insulating Materials for Testing
23 3
D , kg/m ~Notes 2-4!
D 891 Test Methods for Specific Gravity, Apparent, of
3 3
NOTE 4—The SI unit of density, as defined in Practice E 380 is kg/m .
Liquid Industrial Chemicals
3 3
To convert density in g/cm to density in kg/m , multiply by 1000.
D 1505 Test Method for Density of Plastics by the Density-
2 NOTE 5—Specific gravity 23/23°C can be converted to density 23°C,
Gradient Technique
kg/m , by use of the following equation:
D 1622 Test Method for Apparent Density of Rigid Cellular
23 C 3
Plastics D , kg/m 5 sp gr 23/23°C 3 997.6
D 1898 Practice for Sampling of Plastics
4. Summary of Test Method
E 1 Specification for ASTM Thermometers
4.1 Determine the mass of a specimen of the solid plastic in
E 12 Terminology Relating to Density and Specific Gravity
air. It is then immersed in a liquid, its apparent mass upon
of Solids, Liquids, and Gases
immersion is determined, and its specific gravity (relative
density) calculated.
These test methods are under the jurisdiction of ASTM Committee D-20 on
Plastics and are the direct responsibility of Subcommittee D20.70 on Analytical
5. Significance and Use
Methods (Section D20.70.01).
5.1 The specific gravity or density of a solid is a property
Current edition approved Aug. 10, 1998. Published November 1998. Originally
published as D 792 – 44. Last previous edition D 792 – 91. that can be measured conveniently to identify a material, to
Annual Book of ASTM Standards, Vol 08.01.
Annual Book of ASTM Standards, Vol 15.05.
Annual Book of ASTM Standards, Vol 14.03.
5 6
Discontinued; see 1995 Annual Book of ASTM Standards, Vol 15.05. Annual Book of ASTM Standards, Vol 14.02.
*A Summary of Changes section appears at the end of this standard.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 792
follow physical changes in a sample, to indicate degree of 9.2 Sample Holder, corrosion-resistant.
uniformity among different sampling units or specimens, or to 9.3 Sinker—A sinker for use with specimens of plastics that
indicate the average density of a large item. have specific gravities less than 1.000. The sinker shall: (1)be
5.2 Changes in density of a single specimen may be due to corrosion-resistant; (2) have a specific gravity of not less than
changes in crystallinity, loss of plasticizer, absorption of 7.0; (3) have smooth surfaces and a regular shape; and (4)be
solvent, or to other causes. Portions of a sample may differ in slightly heavier than necessary to sink the specimen. The
density because of difference in crystallinity, thermal history, sinker should have an opening to facilitate attachment to the
porosity, and composition (types or proportions of resin, specimen and wire.
plasticizer, pigment, or filler). 9.4 Immersion Vessel—A beaker or other wide-mouthed
vessel for holding the water and immersed specimen.
NOTE 6—Reference is made to Test Method D 1622.
9.5 Thermometer—A thermometer with an accuracy of
5.3 Density is useful for calculating strength-weight and
61°C is required if the test is not performed in the standard
cost-weight ratios.
laboratory atmosphere of Practice D 618, (refer to 17.4).
6. Sampling
10. Materials
6.1 The sampling units used for the determination of spe-
10.1 Water—The water shall be substantially air-free and
cific gravity (relative density) shall be representative of the
distilled or demineralized water.
quantity of product for which the data are required, in
NOTE 8—Water may be rendered substantially air-free by boiling and
accordance with Practice D 1898.
cooling or by shaking under vacuum in a heavy-walled vacuum flask.
6.1.1 If it is known or suspected that the sample consists of
(Precaution: Use gloves and shielding.) If the water does not wet the
two or more layers or sections having different specific
specimen, a few drops of a wetting agent shall be added. If this solution
gravities, either complete finished parts or complete cross
does not wet the specimen, Method B shall be used.
sections of the parts or shapes shall be used as the specimens,
11. Test Specimen
or separate specimens shall be taken and tested from each
layer. The specific gravity (relative density) of the total part
11.1 The test specimen shall be a single piece of the material
cannot be obtained by adding the specific gravity of the layers,
under test of any size and shape that can conveniently be
unless relative percentages of the layers are taken into account.
prepared and tested, provided that its volume shall be not less
than 1 cm and its surface and edges shall be made smooth. The
7. Conditioning
thickness of the specimen should be at least 1 mm for each 1
7.1 Conditioning—Condition the test specimens at
g of weight. A specimen weighing 1 to 5 g usually will be
23 6 2°C and 50 6 5 % relative humidity for not less than 40
found convenient, but specimens up to approximately 50 g may
h prior to test in accordance with Procedure A of Practice
be used (Note 9). Care should be taken in cutting specimens to
D 618, for those tests where conditioning is required. In cases
avoid changes in density resulting from compressive stresses or
of disagreement, the tolerances shall be 1°C and 62 % relative
frictional heating.
humidity.
NOTE 9—Specifications for certain plastics require a particular method
7.2 Test Conditions—Conduct tests in the standard labora-
of specimen preparation and should be consulted if applicable.
tory atmosphere of 23 6 2°C and 50 6 5 % relative humidity,
11.2 The specimen shall be free from oil, grease, and other
unless otherwise specified in the test methods or in this
foreign matter.
specification. In cases of disagreement, the tolerances shall be
1°C and 62 % relative humidity.
12. Procedure
TEST METHOD A FOR TESTING SOLID PLASTICS
12.1 Measure and record the water temperature.
IN WATER (SPECIMENS 1 TO 50 g)
12.2 Weigh the specimen in air to the nearest 0.1 mg for
specimens of mass 1 to 10 g or to the nearest mg for specimens
8. Scope
of mass more than 10 to 50 g.
8.1 This test method involves weighing a one-piece speci-
12.3 Attach to the balance a piece of fine wire sufficiently
men of 1 to 50 g in water, using a sinker with plastics that are
long to reach from the hook above the pan to the support for the
lighter than water. This test method is suitable for plastics that
immersion vessel. Attach the specimen to the wire such that it
are wet by, but otherwise not affected by water.
is suspended about 25 mm above the vessel support.
9. Apparatus
NOTE 10—The specimen may be weighed in air after hanging from the
wire. In this case, record the mass of the specimen, a 5 (mass of
9.1 Analytical Balance—A balance with a precision within
specimen + wire, in air) − (mass of wire in air).
0.1 mg, accuracy within 0.05 % relative (that is, 0.05 % of the
mass of the specimen in air), and equipped with a stationary 12.4 Mount the immersion vessel on the support, and
support for the immersion vessel above the balance pan (“pan
completely immerse the suspended specimen (and sinkers, if
straddle”). used) in water (10.1) at a temperature of 23 6 2°C. The vessel
must not touch wire or specimen. Remove any bubbles
NOTE 7—Assurance that the balance meets the performance require-
adhering to the specimen, wire, or sinker, paying particular
ments should be provided by frequent checks on adjustments of zero point
attention to holes in the specimen and sinker. Usually these
and sensitivity and by periodic calibration for absolute accuracy, using
standard masses. bubbles can be removed by rubbing them with another wire. If
D 792
the bubbles cannot be removed by this method or if bubbles are
where:
continuously formed (as from dissolved gases), the use of
a 5 apparent mass of specimen, without wire or sinker, in
vacuum is recommended (Note 12). Determine the mass of the
air,
b 5 apparent mass of specimen (and of sinker, if used)
suspended specimen to the required precision (12.2) (Note 11).
completely immersed and of the wire partially im-
Record this apparent mass as b (the mass of the specimen,
mersed in liquid, and
sinker, if used, and the partially immersed wire in liquid).
w 5 apparent mass of totally immersed sinker (if used) and
Unless otherwise specified, weigh rapidly in order to minimize
of partially immersed wire.
absorption of water by the specimen.
13.2 Calculate the density of the plastic as follows:
NOTE 11—It may be necessary to change the sensitivity adjustment of
23C 3
D , kg/m 5 sp gr 23/23°C 3 997.6
the balance to overcome the damping effect of the immersed specimen.
NOTE 12—Some specimens may contain absorbed or dissolved gases,
14. Report
or irregularities which tend to trap air bubbles; any of these may affect the
14.1 Report the following information:
density values obtained. In such cases, the immersed specimen may be
14.1.1 Complete identification of the material or product
subjected to vacuum in a separate vessel until evolution of bubbles has
tested, including method of specimen preparation and condi-
substantially ceased before weighing (see Test Method B). It must also be
tioning,
demonstrated that the use of this technique leads to results of the required
14.1.2 Average specific gravity (relative density) for all
degree of precision.
specimens from a sampling unit, reported as sp gr 23/
12.5 Weigh the wire (and sinker, if used) in water with
23C 3
23°C 5 ___, or average density reported as D 5 ___ kg/m ,
immersion to the same depth as used in the previous step
14.1.3 A measure of the degree of variation of specific
(Notes 13 and 14). Record this height as w (mass of the wire in
gravity or density within the sampling unit such as the standard
liquid).
deviation and number of determinations on a homogeneous
material or the averages plus these measures of dispersion on
NOTE 13—It is convenient to mark the level of immersion by means of
different layers or areas of a nonhomogeneous product,
a shallow notch filed in the wire. The finer the wire, the greater the
14.1.4 Report the temperature of the water.
tolerance which may be permitted in adjusting the level of immersion
14.1.5 Any evidence of porosity of the material or speci-
between weighings. With wire Awg No. 36 or finer, disregard its degrees
of immersion and, if no sinker is used, use the mass of the wire in air as men,
w.
14.1.6 The method of test (Method A of Methods D 792),
NOTE 14—If the wire is left attached to the balance arm during a series and
of determinations, the mass a may be determined either with the aid of a
14.1.7 Date of test.
tare on the other arm of the balance or as in Note 12. In such cases, care
15. Precision and Bias
must be taken that the change of mass of the wire (for example, from
visible water) between readings does not exceed the desired precision.
15.1 See Section 23.
12.6 Repeat the procedure for the required number of
TEST METHOD B FOR TESTING SOLID PLASTICS
specimens. Two specimens per sample are recommended.
IN LIQUIDS OTHER THAN WATER (SPECIMENS 1
Determine acceptability of number of replicate test specimens
TO 50 g)
by comparing results with precision data given in Tables 1 and
16. Scope
2 of Section 23. Additional specimens may be required to give
the desired precision.
16.1 Test Method B uses a liquid other than water for testing
one-piece specimens, 1 to 50 g, of plastics that are affected by
13. Calculation water or which are lighter than water.
13.1 Calculate the specific gravity of the plastic as follows:
17. Apparatus
Sp gr 23/23°C 5 a/~a 1 w 2 b!
17.1 The apparatus shall include the balance, wire, and
immersion vessel of Section 8, and, optionally, the following:
TABLE 1 Test Method A Specific Gravity Tested in Water
A B C D
Material Mean S S r R
r R
Polypropylene 0.9007 0.00196 0.00297 0.00555 0.00841
Cellulose Acetate Butyrate 1.1973 0.00232 0.00304 0.00657 0.00860
Polyphenylene Sulfide 1.1708 0.00540 0.00738 0.01528 0.02089
Thermoset 1.3136 0.00271 0.00313 0.00767 0.02171
Polyvinyl Chloride 1.3396 0.00243 0.00615 0.00688 0.01947
A
S is the within laboratory standard deviation for the individual ma
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